1. Field of the Invention
This invention relates to a pneumatic radial tire having an improved high-speed durability while controlling increases of tire weight and cost as much as possible and comprising a tread in which an annular recess portion is arranged in the tread at a given region in the widthwise direction thereof.
2. Description of the Related Art
In general, it is known that a pneumatic radial tire having an annular recess portion in the widthwise center of the tread is particularly excellent in drainage during running at high speeds. Since the drainage increases as the volume of the annular recess portion becomes large, the depth of the annular recess portion in the tire is desired to become deep, but it is restricted by the thickness of the tread. For this end, it is advantageous to make deeper the depth of the annular recess portion by depressing regions of the carcass and the belt at the annular recess portion in the tread inward in the radial direction of the tire and along the circumference of the tread. There are also known pneumatic radial tires satisfying such a requirement.
In the above conventional radial tires, the ends and central portion of the belt are apt to expand in the radial direction of the tire through centrifugal force during running at high speeds, and hence there is caused a fear of generating belt separation by the interaction between the above radial expansion and deformation produced by running under loading to degrade high-speed durability. Therefore, a cap layer covering the full radially outer surface of the belt, a narrow-width layer covering only the end portion of the belt, an auxiliary belt layer covering only the central portion of the belt or the like should be arranged as a belt reinforcing member, which increases the tire weight only by the amount of the belt reinforcing member used as compared with tires having an ordinary belt structure to degrade rolling resistance and fuel consumption. Thus, the conventional radial tires are required to improve high-speed durability without increase of tire weight and cost.